A remote controller attached to home appliances adjustable with a radio wave from a remote controller employs a microwave in order to avoid interference with unwanted electromagnetic wave emitted from various other home appliances, because the frequency of microwave is substantially apart from those of the electromagnetic waves. A microwave oscillating circuit mounted to a remote controller employs a strip-line stub of which tip is open. The strip-line stub is formed by a printed circuit board including a dielectric layer having a uniform dielectric constant and being subject to little loss in order to stabilize oscillating characteristics such as an oscillating frequency, oscillating output power and the like. A "kotatsu" is one of those home appliances adjustable with a microwave from a remote controller. A "kotatsu" is a Japanese traditional heating appliance used mostly in a living room. The constitution of "kotatsu" is explained in general in Prior Art of U.S. Pat. No. 4,449,034.
In the kotatsu, a remote controller is integrated into a top plate of the kotatsu and transmits a weak microwave signal modulated by a control signal to a receiver. The receiver integrated into a kotatsu body receives and demodulates the microwave signal, and the resultant signal controls a temperature of heating element of the kotatsu. Disperses of components characteristics transistors' characteristics among others making up the microwave oscillating circuit cause a disperse of an oscillating frequency. Since a control sensitivity of respective remote controllers is subject to the disperse, each product eventually has its own dispersion. In order to suppress this dispersion of the oscillating frequency, a bandwidth of a band-pass-filter in the receiver has been widened; however, the resultant receiver has been vulnerable to noises and unwanted electromagnetic waves. This method is, therefore, not appropriate to overcome the problem. Other methods described below have been employed to overcome the problem discussed above.
(1) Variable inductance 82A is added to an oscillating circuit as shown in FIG. 8A; however, this not only enlarges a size of a remote controller but also boosts the cost.
(2) Japanese Patent Application Non-examined Publication No. H05-335833 discloses that conductive small lands 85A-85E powered in advance are disposed in resonator 85, one of elements making up an oscillating circuit, as shown in FIG. 8B. The small lands are physically separated from resonator 85 by a laser cutter thereby varying an electrical length of resonator 85 so that an oscillating frequency can be adjusted. This method, however, requires an expensive precision apparatus such as a laser cutter.
(3) Japanese Patent Application Non-examined Publication No. H09-162642 discloses that tip-open type stubs 88A are provided in resonator 88 and conductive patterns 88B are disposed near resonator 88 in advance, where resonator 88 is coupled to strip-line stub 87 which connected to circuit 86 as shown in FIG. 8C. Those elements are electrically connected with solder or bonding wires thereby adjusting an oscillating frequency. This method, however, results in lowering reliability of the oscillating circuit because it requires solder bridges. Further, this method needs an expensive precision apparatus such as a wire-bonder.